Spring的IOC容器

基于spring framework 4.x， jdk1.8

1.集成Spring到项目中

IOC容器需要以下spring核心依赖项：spring-core, spring-beans, spring-context, spring-expression

创建maven项目，并引入spring核心依赖以及单元测试junit到pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>example</groupId>
    <artifactId>Spring</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>4.3.18.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>4.3.18.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.3.18.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-expression</artifactId>
            <version>4.3.18.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>compile</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

2.新建spring配置文件spring.xml在main/resources文件夹下

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:util="http://www.springframework.org/schema/util"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/util
       http://www.springframework.org/schema/util/spring-util.xsd">


</beans>

3.新建一个测试类com.example.test.MainTest在main/java下

package com.example.test;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainTest {
    
}

2.基于XML配置Bean

2.1通过反射配置Bean

1.通过全类名反射的方式在ioc容器中创建bean

新建一个JavaBean对象com.example.bean.Bean在main/java下，通过全类名反射的方式需要bean实现无参构造器

package com.example.bean;

public class Bean {
    private String name;

    public Bean() {
        System.out.println("bean 无参构造");
    }

    public Bean(String name) {
        System.out.println("bean 有参构造");
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Bean{" +
                "name='" + name + '\'' +
                '}';
    }
}

spring.xml中通过<bean>配置bean，class设置为bean的全类名，id用于引用bean，id在ioc容器中必须是唯一的

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:util="http://www.springframework.org/schema/util"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/util
       http://www.springframework.org/schema/util/spring-util.xsd">

    <bean id="bean" class="com.example.bean.Bean">
       <property name="name" value="lzj"/>
    </bean>

    <bean id="bean2" class="com.example.bean.Bean" p:name="lzj"/>

</beans>

Spring提供了两种ioc容器的实现，BeanFactory和ApplicationContext，BeanFactory是ioc容器的基本实现，ApplicationContext是BeanFactory的子接口，提供了更加高级的特性

ApplicationContext的主要实现类有

• ClassPathXmlApplicationContext 从类路径下加载配置文件
• FileSystemXmlApplicationContext 从文件系统加载配置文件
• WebApplicationContext 专门为web应用所准备，从web根目录的路径中完成初始化

ApplicationContext在初始化上下文时就会实例化所有单例的Bean

package com.example.test;

import com.example.bean.Bean;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainTest {
    @Test
    public void testBean() {
        // 根据spring.xml配置文件启动spring-ioc容器，ioc容器启动，并且会调用无参构造器
        ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");

        //从ioc容器中获取bean实例
        Bean bean = (Bean) context.getBean("bean");
        System.out.println(bean);

        Bean bean2 = (Bean) context.getBean("bean2");
        System.out.println(bean2);
    }
}

输出

bean 无参构造
Bean{name='lzj'}
bean 无参构造
Bean{name='lzj'}